Inverter/Isolator problem

[Robert W Carlson]

We have a 1996 Marquis.  While driving I cannot use the inverter or the generator.  Both will overcharge the house batteries.  The chassis battery runs down to 8 volts and all the alarms go off.  The inverter works o.k. with or without shore power.  The ignition key has a position for charging which connects the chassis and house batteries together, which is working.  Bend tells me that the isolator was uniquely wired so all batteries are connected while driving.  I think the isolator has failed, although Bend tells me it is "bullet proof".  I have disconnected the high amp cable at the fuse block marked "coach batteries" while driving and insulated it so I can use the generator and the chassis battery stays charged.  However, I don't think I am charging the house batteries while on the road.  Any ideas as to whether the problem could be in the inverter or the isolator?  

Bob & Carol Carlson

[Gerald Farris]

From what I can tell about your complaint, it sounds like your engine alternator is not charging. The best way to test the alternator voltage output is to charge-up all batteries, unplug shore power, start the engine and run it while checking the voltage at the house batteries and the chassis batteries. The voltage should be 13.8 to 14.2 volts on both sets of batteries. If the batteries are not fully charged the voltage will be a little less depending on how low their state of charge is. If the voltage is the same on both sets of batteries with the engine running or not, check the voltage on the alternator terminal (usually the center one) of the isolator. If that voltage is low (12v or less) or 0, you have a bad connection or a bad alternator. If one battery bank is low and one is high. you have a bad connection between the isolator and the batteries or a bad isolator. If both battery readings are low but the alternator terminal is high, you have a bad isolator or both connections from the isolator to the batteries are bad.  

The inverter does not charge the chassis batteries. The chassis batteries can only be charged by the inverter when all batteries are connected together (hold down the boost switch or turn the key to the left on your coach). I hope this helps.

Gerald